The proposed research includes studies of morphological organization in the mammalian visual system and consists of a two front investigation of the dorsal lateral geniculate nucleus, the main thalamic relay between the retina and the primary visual cortex. The results will provide new information concerning: 1) the morphological basis of the functional organization of the visual system; 2) the consequences of neuronal damage on the structure of axons and dendrites of intact, deafferented cells; and 3) the capacity of developing neurons to reorganize after injury in the central nervous system with emphasis on the importance of this reorganization for maintaining neuronal structure and function. The first set of experiments will reveal features about the normal organization of the lateral geniculate nucleus in cats and monkeys. Light microscopic and electron microscopic studies will examine the morphology of lateral geniculate neurons and the structure of axons to the nucleus from the retina and the visual cortex. These studies address basic issues concerning the role of the thalamus in processing sensory information. The results should further our understanding of the intrinsic organization of the lateral geniculate nucleus; the role of cortical feedback in the thalamus; and the relationship between neuronal structure and function. The second set of experiments will examine effects of deafferentation. They are designed to show changes in the normal organization of the lateral geniculate nucleus following interruption of the input from one retina. Such denervation in adult animals results in atrophy of all deafferented neurons and proposed experiments will show the consequences of this atrophy on dendritic and axonal morphology. The same denervation in young animals, however, can result in some deafferented neurons that do not atrophy. That is, neurons in these young animals seem to have a capacity for reorganization that results in the prevention of the atrophic effects of denervation. Experiments described in this proposal will explore this reorganization and determine if changes in the structural features of axons and dendrites correlate with the prevention of atrophy.